The present invention relates to a device for localizing acoustic sources and measuring their intensities.
Acoustic comfort appears to be a significant problem today, particularly in the case of residents living in urban areas or near an airport.
In order to abate vehicle noise, it is necessary to better understand the various acoustic phenomena occurring in the outer envelope of the vehicle. Certain areas of a vehicle appear to be the sources of harmful noise. For example, in the case of an aircraft, the engines and landing gear are areas particularly likely to emit noise. However, other areas may also be involved although their intensity is generally less.
Therefore, it is important to localize not only the high-intensity noise sources but also the lower-intensity sources. The precise location and measurement of their intensities then enable less-noisy systems, systems more adapted to daily life, to be developed.
Known measuring devices employ a microphone array and means for processing the signals coming from the various microphones. The usual signal processing method is to establish an acoustic source hologram, i.e., a distribution of acoustic pressures, or intensities, at various computation points on a given surface, creating, for each computation point in the hologram, the sum of the acoustic pressures measured by the microphones, taking into account the lag in acoustic pressure corresponding to the travel time between the computation point and a microphone.
The hologram, as described above, is made up of lobes corresponding to the positions of the acoustic sources, and lobes due to the limited size of the antenna. These are called main lobes and secondary lobes, respectively.
By means of these systems, the localized acoustic sources obtained have a resolution that is higher in proportion to the frequency, and to the size of the antenna that is composed of microphones.
However, problems arise in the case of sources emitting at high frequencies. In this case, the mesh size of the antenna, i.e., the microphone spacing, must be sufficiently small. If this is not the case, parasitic lobes known as image lobes appear on the hologram in addition to the real sources. To prevent such a phenomenon, the use of a large number of microphones is essential, increasing the costs of implementing such a device.